1. Field of the Invention
The present invention relates to a fuel injector with an integrated spark plug for a direct injection type engine.
2. Description of the Related Art
A fuel injector with an integrated spark plug is developed to be used in a direct injection type engine.
It is required that a fuel injector with an integrated spark plug supplies desired amount of fuel, at a desired timing as a fuel injector and induces a spark discharge with desired intensity, at a desired timing and desired position, as a spark plug.
A fuel injector with an integrated spark plug becomes very hot because the end part of the device is exposed in a combustion chamber and a spark discharge is induced there.
If spark discharge occurs close to a outer surface of a needle housing, the needle housing is made very hot. Therefore, fuel which contacts inner surface of the hot needle housing is heated and tar will deposit in the fuel and the fluidity of the fuel will be deteriorated, so that it will be difficult to inject the fuel adequately.
If an electrode is disposed in the path of a fuel spray injected from a nozzle of injector, fuel will stick to the electrode, then will be exposed in the combustion gas, carbon will deposit on the electrode, and it will be difficult to induce a suitable spark discharge because the gap is not adequate.
Therefore, attention should be paid to the position of the spark discharge in a fuel injector with an integrated spark plug.
Also, it is important to maintain the alignment of the elements which compose a fuel injector with an integrated spark plug in order that the fuel may be injected adequately.
In addition to these points, attention should be paid to the insulation between the electric conductors and other metallic elements so that the solenoid operates correctly to activate needle valve, and so that an adequate spark discharge is induced.
In the fuel injector with an integrated spark plug disclosed in the Japanese Unexamined Utility Model Publication [KOKAI] No. 63-154760 (shown in FIG. 5), the fuel passage which is disposed between a yoke and a housing is not symmetrically arranged around the center axis, so that fuel contained inside of the fuel injector is unequally cooled. Therefore, it is feared that strain occurs and the elements do not align accurately and, as a result, fuel is not injected adequately.
Also, the above type fuel injector with an integrated spark plug has insufficient insulation between a central electric conductor and a solenoid. Therefore, it is possible that a high voltage electric current leaks from "e.sub.1 " to "e.sub.2 " (shown in FIG. 5) and is applied to the solenoid and, as a result, an adequate spark discharge and an adequate injection of fuel is not attainable.
In the fuel injector with an integrated spark plug disclosed in the Japanese Unexamined Patent Publication [KOKAI] No. 4-54275, a spark discharge occurs outside of the wall of injector inside of which fuel is contained, therefore the fuel is heated and tar will deposit.